Field of the Invention
The present invention relates to a process for treating a gas by adsorption, of the type in which a pressure swing adsorption treatment unit, commonly known as a PSA unit, is used, and more particularly PSA units using at least 5 adsorbers.
Related Art
Generally, a gas-phase adsorption process makes it possible to separate one or more molecules of a gas mixture containing them, by exploiting the difference in affinity of one or more adsorbents for the various constituent molecules of the mixture. The affinity of an adsorbent for a molecule depends, on the one hand, on the structure and the composition of the adsorbent and, on the other hand, on the properties of the molecule, in particular its size, its electronic structure and its multipole moments. An adsorbent may be, for example, a zeolite, an activated carbon, an activated alumina which is optionally doped, a silica gel, a carbon-based molecular sieve, a metalloorganic structure, an alkali metal or alkaline-earth metal oxide or hydroxide, or a porous structure preferably containing a substance capable of reacting reversibly with the molecules, a substance such as amines, physical solvents, metallic complexing agents, metal oxides or hydroxides, for example.
The most conventional adsorbent materials are in the form of particles (beads, rods, crushed materials, etc.) but also exists in structured form, such as monoliths, wheels, parallel-passage contactors, fabrics, fibres, etc.
Three major adsorption process families can be distinguished: lost-charge processes, temperature swing adsorption processes known as TSA and, finally, PSA (Pressure Swing Adsorption) processes.
In lost-charge processes—reference is often made in this case to a guard bed—a new charge is put in place when the one being used is saturated with the impurities or more generally when it can no longer sufficiently perform its protective role.
In TSA processes, the adsorbent at the end of use is regenerated in situ, i.e. the impurities that have been stopped are discharged so that said adsorbent recovers most of its adsorption capacities and can recommence a purification cycle, the essential regeneration effect being due to an increase in temperature.
Finally, in PSA processes, the adsorbent at the end of the production phase is regenerated by desorption of impurities, obtained by means of a decrease in their partial pressure. This decrease in pressure can be obtained by means of a decrease in the total pressure and/or by sweeping with a gas which is free of impurities or which contains few impurities.